1. Field of the Invention
The present invention relates to luminous glass ceramics containing rare earth elements in a glass phase and/or a crystallized phase, wherein thermal conductivity, a character of thermal expansion, mechanical strength, of the luminous glass ceramics are improved and further having various emission wavelengths. In particular, the invention relates to luminous glass ceramics which can be suitably applied to an oscillation medium for laser oscillation, an excitation light filter or the like.
2. Description of Related Art
For materials which are used as the luminous materials in earlier technology, a glass material, a single crystal material, and a ceramic material have been known.
However, there are problems of the thermal conductivity and the thermal expansion in the glass material. That is, because the glass material has low thermal conductivity and a high coefficient of thermal expansion, when the glass material is subjected to irradiation by an excitation light with high intensity, there is a problem that the glass material breaks under thermal expansion thereof because occurred heat is hard to escape therefrom. When the glass material is used under such environmental circumstances, temperature of which is largely or rapidly changed, there is a problem that the glass material breaks under thermal fatigue thereof.
For example, the luminous glass material which is applied to the oscillation medium for laser oscillation or the wavelength conversion filter for excitation light of laser breaks under the thermal stress because the thermal conductivity of the glass material is low and the temperature distribution thereof becomes non-uniform when the glass material is subjected to irradiation by the laser.
On the other hand, there are problems for the single crystal material that it is difficult to uniformly dope the optically active element to the single crystal material and to produce a practically large size of product of the single crystal material. There is a problem that the ceramic material is liable to occur a light scattering caused by grain boundaries and pores, of the ceramic material, which is character thereof.